some oil on my plug thread.

[Shotgun28]

I was looking over my baby(stored for winter) the other day and noticed some oil on one of my plug threads, I am not sure what number it is, furthest one back on the passenger side, any ideas> I just bought some new heads and might have a better idea when putting them in, but would like some info on what to look for. This is driving me crazy. Thank you

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91 LX Convertible Gray on Red B&M Shift improver kit,ASP red alum. underdrive pulleys, Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and just purchased some GT40P heads, looking at exhaust, Lentech Street Terminator plus on it's way...